This paper examines the mechanical principle of the roadway driving along next goaf in coal face with fully mechanized top-coal caving. On the basis of analyzing mechanical situation of the roadway, a mechanical model of roadway floor is established. Applying the elastic theory, the relative vertical displacement of floor strata of the roadway, the narrow pillar and the high abutment zone are calculated. The mechanical principle of floor heave of the roadway is revealed.
The coal face with fully mechanized top-coal caving is a kind of face in which the coal face is arranged in the lower portion of a thick coal seam and the top coal above the supports is destroyed by ground pressure and drops down by its own gravity. The roadway driving along next goaf is a kind of gateway which is driven along gob of next face with a narrow chain pillar of 3-5 meters wide. This is a new technique of gateway arrangement. The mechanical situation of the roadway is different from that of average gateway. On one side of the roadway is the relative integrated coal seam (hereafter 'integrated coal') and on the other side is the narrow pillar in which plastic deformation has occurred.
The high abutment pressure zone on the integrated coal beside the roadway will form due to superposition of the advancing abutment pressure in front of working face and the concentration stress of the gob side in the course of extraction. The stress on the integrated coal is much greater than that on any side of the average gateway. Intensive heaves often occur in these roadways. However, the mechanism of floor heave of the roadway is different fi'om that of the average gateway. In order to control the floor heaves efficiently, it is necessary to study the mechanical principal of floor heave of the roadway.
According to the key stratum theory and movement pattern of the overlying strata on gob side of coal face with fully mechanized top-coal caving, the main stratum will fracture and form an articulated beam on gob side after next face is pushed forward, which is called 'big structure'. The side concentration stress will form on the coal seam of working face. Meanwhile, the stress-reducing zone of the gob side will form, roadway will be driven in the zone (Figure 1)
Because of the coal seam along the next gob subjected to given deformation of the big structure, the fracture and plastic zone of 2-4 meters wide will form at the edge of coal seam before driving roadway. The width of chain pillar is only 3-5 meters, therefor the chain pillar will basically be in plastic status after the roadway is driven.
In the course of extraction, the stress equilibrium of the big structure will be disturbed by advancing abutment pressure, whose block B will be rotaries again, the narrow pillar will wholly be in fracture status, its load-beating capacity will be further reduced. Meanwhile, because of superposition of the advancing abutment pressure and the concentration stress of the gob side on integrated coal beside the roadway, the stress on the integrated coal will increase.